Sunken or cracked concrete around Austin can often be lifted with slurry or foam, sealed, ground or resurfaced. Expansive clay is a frequent cause, so a good repair also deals with drainage and soil moisture, and timing can matter after a drought. Badly broken slabs are better replaced, and cracks inside the house call for a structural engineer first.
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A cracked or uneven slab doesn't always need to come out. Depending on why it failed, concrete can often be lifted, sealed, patched or resurfaced with less mess and cost than replacement. In Central Texas, though, the cause is often the soil itself, and a repair that ignores that tends not to last.
Why concrete cracks and moves around Austin
- Expansive clay. The blackland clays common east of I-35 swell when wet and shrink when dry. After a long drought, slabs can drop at the edges; after a wet season, they can heave.
- Loose fill. Soil placed around new homes during construction, often next to foundations, garages and steps, can settle for years.
- Runoff. Downspouts and heavy storms can wash base material out from under slab edges, leaving voids.
- Tree roots. Live oaks, pecans and elms lift walks and driveway edges, and roots also draw moisture from clay, which can make it shrink nearby.
- Rock and fill pockets. On Hill Country lots, a slab may sit partly on limestone and partly on fill. The fill side settles; the rock side doesn't.
- Shrinkage and heat. Fast drying on hot days and joints spaced too far apart cause random cracking.
Repair options
- Slab lifting with cement slurry (mudjacking): a grout is pumped under the slab through drilled holes to raise it and fill voids.
- Polyurethane foam lifting: expanding foam injected through smaller holes. It's light and cures quickly.
- Crack and joint sealing: flexible sealants keep water out of the base, which matters on clay.
- Grinding: shaving down a raised edge to remove a trip hazard.
- Patching and resurfacing: for chipped, spalled or worn surfaces on a slab that is otherwise sound.
- Section replacement: cutting out broken panels at the joints and pouring new concrete.
When lifting makes sense
Lifting works best when a slab is mostly intact and sank as one piece. On expansive clay, it's worth asking whether the movement has stopped. If a slab dropped during a drought, the soil may swell back somewhat when wet weather returns, so the timing of a lift and what's done about moisture both matter. Extending downspouts, regrading so water drains away, and keeping soil moisture more even near slabs are often part of a good repair plan.
Trip hazards and public sidewalks
A raised joint on a walk or driveway is a common cause of falls. If the hazard is on a public sidewalk, check with your city about responsibility and permits first. Inside the City of Austin, sidewalk and driveway work in the right-of-way needs a permit and a contractor with the city's Right-of-Way Contractor license.
When it might be the foundation
Many Austin homes sit on slab-on-grade foundations over the same clay that moves driveways and patios. Cracks in flatwork are usually not structural. But cracks in interior floors or walls, stair-step cracks in brick or stone veneer, gaps at window frames, or doors that suddenly stick can mean the house itself is moving. Have a structural engineer evaluate that first. Foundation repair is a separate specialty, and flatwork repairs won't solve it.
Questions to ask
- What do you think caused this, and how does the repair deal with it?
- Lift, patch or replace, and why?
- Is my soil still moving, and does the timing of the repair matter?
- What does the warranty cover if the slab settles again?
Have a sunken slab or trip hazard? Mark your request as urgent and request a concrete repair contractor. If the whole driveway is failing, see driveway replacement.
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Frequently asked questions
Should I lift a slab that sank during a drought?
Ask your contractor. On expansive clay, soil that shrank in drought may swell back somewhat after wet weather. Some contractors prefer to wait or to fix drainage first. The right answer depends on the slab and how much it has moved.
Is mudjacking or foam lifting better?
Both can lift sunken slabs. Cement slurry is long established and often less expensive; polyurethane foam uses smaller holes, is lighter and cures quickly. The best choice depends on the slab, the voids and the contractor's experience.
Are driveway cracks a sign of foundation problems?
Usually not. Flatwork cracks are common on Central Texas soils. Cracks inside the house, stair-step cracks in brick or stone, or doors that start sticking are signs to have a structural engineer look at the foundation.
Sources and further reading
- American Concrete Institute (ACI)
- Portland Cement Association (PCA)
- Bureau of Economic Geology, UT Austin: Mount Bonnell and the Balcones Fault Zone
- City of Austin Transportation and Public Works: Right-of-Way Contractors
- City of Austin Development Services: Trees on Residential Property
- TCEQ: Edwards Aquifer rules for private residences
- City of Georgetown permits
- City of Leander: Driveway permit submittal packet
- City of Lakeway: Building applications and fees
- TxDOT Access Management Manual: Driveway permits
- Texas Department of Licensing and Regulation (TDLR)
- Texas811: Call before you dig